DemandForwarder

A DemandFillerIfc that doesn't fulfil demands from local stock — instead it forwards each incoming demand to an upstream supplier, waits for delivery, and runs a user-supplied callback when the upstream delivers. Analogous to a real-world freight forwarder or drop-shipper: takes the order, places it with a supplier, takes delivery, hands the goods to the original customer.

Typical use is to assign a DemandForwarder to a routing node's demandFiller slot. When the network sends a demand to that node, the forwarder receives it for processing, propagates an equivalent request upstream, and on upstream delivery runs whatever finalisation the node needs (typically original.fulfillAndDispatch(carrier) to ship the original onward, or letting a receiving-dock mechanism handle it).

On receive(demand) the forwarder:

1. Receives the demand for processing via receiveForProcessing — the demand transitions to IN_PROCESS and waits here for upstream delivery.

2. Sends an equivalent request to the upstream filler resolved by upstreamSupplier.

3. When the upstream receives the forwarded request, the forwarder asks the upstream to fill it (filler.fillDemand(...)) unless shouldFillOnReceive returns false (used to opt out for upstreams that drive their own fill cycle, like a routing facility).

4. When the upstream eventually delivers the forwarded request, onUpstreamDelivered is invoked (if non-null) with the original demand — the node now does whatever is needed to complete it (typically fulfil and dispatch via the node's outbound carrier).

The forwarder is itself a persistent DemandFillerIfc — its remaining surface (fillDemand, negotiate, item-type predicates, etc.) is routing-only stubs.

Parameters

See also